Discovering hidden sectors with mono-photon Z' searches

TL;DR

This paper explores the potential to detect hidden sector particles via an invisibly decaying Z' boson at the LHC, proposing a mono-photon search strategy and analyzing background/systematic challenges.

Contribution

It introduces a method to identify hidden sector states through mono-photon Z' searches, extending previous Z Z' analyses and emphasizing systematic error control.

Findings

Hidden Z' decays can be observed at 5 sigma with 50 fb^{-1} for 1 TeV mass.

Detection of a 1.5 TeV Z' requires 1 ab^{-1} of data.

Systematic errors, especially PDF uncertainties, are critical for maximizing search sensitivity.

Abstract

In many theories of physics beyond the Standard Model, from extra dimensions to Hidden Valleys and models of dark matter, Z' bosons mediate between Standard Model particles and hidden sector states. We study the feasibility of observing such hidden states through an invisibly decaying Z' at the LHC. We focus on the process pp -> \gamma Z' -> \gamma X X*, where X is any neutral, (quasi-) stable particle, whether a Standard Model (SM) neutrino or a new state. This complements a previous study using pp -> Z Z' -> l+ l- X X*. Only the Z' mass and two effective charges are needed to describe this process. If the Z' decays invisibly only to Standard Model neutrinos, then these charges are predicted by observation of the Z' through the Drell-Yan process, allowing discrimination between Z' decays to SM neutrinos and invisible decays to new states. We carefully discuss all backgrounds and systematic errors that affect this search. We find that hidden sector decays of a 1 TeV Z' can be observed at 5 sigma significance with 50 fb^{-1} at the LHC. Observation of a 1.5 TeV state requires super-LHC statistics of 1 ab^{-1}. Control of the systematic errors, in particular the parton distribution function uncertainty of the dominant Z \gamma background, is crucial to maximize the LHC search